ADAU1701 in self-boot mode --- mistake in my board design

Having made a mistake in my board design, I'd like to figure out whether I can (reasonably easily) get around it and make it work.

As indicated in the subject, I'm using the ADAU1701 with an external EEPROM for self-boot.  The circuit is similar to the ADAU1701 mini evaluation board, so I will program the ADAU with a USBi from SigmaStudio.

The mistake I made is that I placed a chip that is driving the RESET line  (without jumper or switch to selectively disconnect it).  The RESET line (the one that goes to the ADAU1701, labeled AUDIO_RESET in the schematic, shown below) is being held at logical 0.  The one that comes from the USBi  (labeled AVR_RESET in the schematic), at this point has absolutely no effect --- it is connected to the RESET pin of an AVR microcontroller, with a 10k pullup.

SigmaStudio cannot connect to the board to download the compiled model, or save latest compilation to EEPROM.  In either case, it "freezes" and when interrupted it reports it could not connect.

I am supplying power to the board  (separately --- a 12V input goes to a 3.3V DC/DC switching regulator).  Those 3.3V go to the ADAU1701 and to the EEPROM.

Below are the relevant sections of the schematic --- the connections to the USBi and the related ADAU1701 pins.

Question #1:  should it work, with the ADAU1701 RESET line being held to 0  (active) ??
Question #2:  any suggestions to get around the problem?

Thanks!

ADAU1701 to USBi connections

ADAU1701 connections

  • Looks like I may have solved the problem --- what I should have done in the first place was to place a jumper between the pin that drives the AUDIO_RESET signal, and the ADAU;  so, it occurred to me that the easiest thing to try was based on that:  I just cut the trace (fortunately it is on the board's top layer), and SigmaStudio could save the latest compilation to EEPROM.  (now I just need to put a small blob of solder to re-connect it)

    I haven't verified that the whole thing works (I don't have the necessary equipment here --- will try it tomorrow at the office), but this ia definitely a good sign!

    Cheers,
    Carlos
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  • Actually, there is still some problem with the design.

    I'm using SigmaStudio 3.17 on Windows 7, through a VirtualBox virtual machine.  This setup so far has worked fine with the ADAU1701 EVAL-MINI board.

    I tried a simple 2-way crossover, getting input from I2S and outputting to the DACs.

    I can do "Write latest compilation to E2PROM",  but when I do "Check last compilation vs. E2PROM", it reports a discrepancy.  The pop-up window shows: 

    FIRST MISMATCH VALUE:  FF AT INDEX: 0.
    DIFFERS FROM EXPECTED VALUE: 01

    As you can see in the schematic above, I used the 24AA256 E2PROM, same as the EVAL-MINI board to be on the safe side.  Any ideas of why I'm getting this error?  What should I try next?

    Thanks,
    Carlos
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  • +1
    •  Analog Employees 
    on Jan 22, 2019 9:49 PM over 1 year ago

    Hello Carlos,

    Sorry for the problems. There are a few other details to take care of.

    The Write Protect is being puled up. This is not a problem during normal operation but it is a problem when you are trying to write to the EEPROM. So you need to pull down the WP pin to allow the EEPROM to be programmed. The connection to the ADAU1701 is there to allow the DSP to pull down the WP line when it writes-back the interface registers when triggered.

    What I have done in designs is to place a transistor in the design to pull down the write protect. The base of the pre-biased transistor is connected to the USBi-5V Power pin. So when you plug in the USBi it pulls down the WP pin. No jumper required.

    So for right now if you can solder on a jumper to pull it down to ground while you are working on it then remove it when you are done.

    Let me know if this works for you.

    Dave T

  • Thanks Dave for your reply and the tips!

    Couple of follow-up questions/comments:

    1. How is this handled in the ADAU1701 EVAL-MINI board?  The ADAU1701 datasheet states "The ADAU1701 does not self-boot if WP is set low" --- the transistor trick you suggest is consistent with this;  but the EVAL-MINI board schematic is not.  In the evaluation board there is switch S5, which allows selection between connecting WP to GND, or to a 10k pullup resistor.  As the schematic shows, S5 connects to the 10k pullup --- I understood that to mean that the board's factory default is that  (WP connected to a 10k pullup), which is why I designed my board like that.

      Right now, the switch (S5) on my evaluation board is to the side of the header connector J8 --- should I guess that that corresponds to connecting the EEPROM's WP to GND?  :-(

      One thing I can't understand is how can the EVAL-MINI board work --- I can't remember whether I changed the position of S5 w.r.t. the factory default;  but I'm somewhat certain that I never change it back and forth when playing with it.  And I am quite sure that I have programmed it, reprogrammed it, tried many different things, powered off then on to verify that the contents downloaded to the EEPROM still take effect, etc.   How can that be?  If I set S5 to the 10k pullup position, then I wouldn't be able to program the EEPROM;  and if I set it to GND, then the ADAU1701 would not do self-boot, so a power cycle would wipe out the design I programmed.   Am I missing something?

    2. Can I get away with downloading the SigmaStudio design into the ADAU1701 without programming the EEPROM?   I would like to test whether the operation is fine  (audio outputs, I2S signals connected correctly, etc.).  I will need to work on a second iteration of this board, so I would like to figure out all of the bugs/glitches  (in any case, as many as possible).   I mean, I will try to solder the jumper as you suggest;  but it looks a bit challenging --- the EEPROM is, like, 3mm away from the WP pin of the ADAU1701, and it connects nowhere else;  do keep in mind that I do not have strong skills (read: good enough eyesight and steady enough hands!) when it comes to soldering tiny things.

      If I try "Link / Compile / Download", the software tells me that that option is for evaluation hardware only;  I can do "Link / Compile / Connect", which I guess I need to do anyway before attempting to program the EEPROM.

      Is that option related to what I'm asking here?

    Thanks,
    Carlos
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  • Just to double check that I understand correctly --- what you're suggesting is what the schematic below shows, right?  Pin 4 of the USBi connector brings in the +5V, correct?  (the transistor can have pretty much any β / hFE --- something as low as 1 still guarantees that the transistor saturates)

    Driving ADAU1701 WP pin from the USBi connection

    Thanks,
    Carlos
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